A quick rundown of the designs:
TL
Main Box Vol 0.94 CuFt
Line X-Section Area 50.27 SqIn
Line Length 2.69′
Weight of damping material (inside line) .47 lbs
Tuned to 37.7 Hz with an approximate 6dB roll off
(This is based on a constant area line X-Section. You can make it more like a horn by using the center point of the line as a pivot and squishing one end a bit while expanding the other end the same amount. I’ve seen designs where either end is the output, depending on if they want more velocity (smaller) or more acoustic coupling (larger).)
Ported
Box Vol 1.5 CuFt
Box, Port and F3 37.8 Hz (unusual, but it is a function of Qts)
3″ port 6-2/3″ long
Like I said above, this is just a starting point to give you and idea of how you might want to proceed. The next step would be to go ahead and use WinISD and HornResp, and definitely read up on sites like https://transmissionlinespeakers.com/en/articles/ to get a better grasp on your idea.
